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ABSTRACT
Correlations allowing the calculations of the convective heat transfer coefficient on all elements of an electronic assembly are proposed in this work. The active element is a Quad Flat Non-Lead-type QFN32 package that may be welded in any position of a printed circuit board (PCB) inclined with respect to the horizontal at an angle ranging from 0° (horizontal position) to 90° (vertical position) by steps of 15°. The power generated by the QFN32 varies between 0.1 W and 0.8 W, corresponding to its normal operating range. Six distinct surfaces are considered in this work and the power exchanged between each of them and the environment is quantified. This survey details a previous one in which it is quantified the global convective heat transfer concerning the whole assembly. The correlations proposed in the present work provide a better modeling of this conventional device widely used in electronic applications. They thus optimize its design while controlling its temperature during operation.
Nomenclature
| = | area of the QFN package’s rear face (m2) | |
| a | = | thermal diffusivity of the air (m2s−1) |
| = | specific heat at constant pressure (J kg−1K−1) | |
| = | dimensionless unit vector opposite to the gravity direction | |
| g | = | gravity acceleration ( m s−2) |
| = | local convective heat transfer coefficient of the ith element (Wm−2K−1) | |
| = | average convective heat transfer coefficient for a given area (Wm−2K−1) | |
| = | average convective heat transfer coefficient of the QFN package’s rear face (Wm−2K−1) | |
| k(α) | = | coefficient of the |
| L | = | characteristic length (m) |
| n(α) | = | coefficient of the |
| P | = | generated power (W) |
| = | convective power exchanged by a given area (W) | |
| = | ratio defined by | |
| = | convective powers exchanged by the QFN package’s top and side faces, respectively (W) | |
| Pr | = | Prandtl Number (–) |
| p | = | pressure (Pa) |
| = | dimensionless pressure (–) | |
| = | heat flux for the ith element (Wm−2) | |
| Ra | = | Rayleigh number (–) |
| T | = | temperature (K) |
| = | temperature of the cavity’s walls and initial temperature of the whole system (K) | |
| = | average QFN package’s surface temperature (K) | |
| = | local temperature of the ith wall element (K) | |
| = | dimensionless temperature (–) | |
| = | average temperature of the QFN package’s rear face (K) | |
| = | velocity vector | |
| = | dimensionless velocity vector | |
| (x, y, z) | = | Cartesian coordinates (m) |
| = | dimensionless coordinates (–) | |
| α | = | inclination angle of the QFN package with respect to the horizontal (°) |
| β | = | air volumetric expansion coefficient (K−1) |
| = | dimensionless nabla operator (–) | |
| = | dimensionless Laplacian operator (–) | |
| ϕ | = | volumetric heat flux (Wm−3) |
| λ | = | air thermal conductivity (Wm−1K−1) |
| µ | = | air dynamic viscosity (Pa s) |
| ρ | = | air density (kg m−3) |
Nomenclature
| = | area of the QFN package’s rear face (m2) | |
| a | = | thermal diffusivity of the air (m2s−1) |
| = | specific heat at constant pressure (J kg−1K−1) | |
| = | dimensionless unit vector opposite to the gravity direction | |
| g | = | gravity acceleration ( m s−2) |
| = | local convective heat transfer coefficient of the ith element (Wm−2K−1) | |
| = | average convective heat transfer coefficient for a given area (Wm−2K−1) | |
| = | average convective heat transfer coefficient of the QFN package’s rear face (Wm−2K−1) | |
| k(α) | = | coefficient of the |
| L | = | characteristic length (m) |
| n(α) | = | coefficient of the |
| P | = | generated power (W) |
| = | convective power exchanged by a given area (W) | |
| = | ratio defined by | |
| = | convective powers exchanged by the QFN package’s top and side faces, respectively (W) | |
| Pr | = | Prandtl Number (–) |
| p | = | pressure (Pa) |
| = | dimensionless pressure (–) | |
| = | heat flux for the ith element (Wm−2) | |
| Ra | = | Rayleigh number (–) |
| T | = | temperature (K) |
| = | temperature of the cavity’s walls and initial temperature of the whole system (K) | |
| = | average QFN package’s surface temperature (K) | |
| = | local temperature of the ith wall element (K) | |
| = | dimensionless temperature (–) | |
| = | average temperature of the QFN package’s rear face (K) | |
| = | velocity vector | |
| = | dimensionless velocity vector | |
| (x, y, z) | = | Cartesian coordinates (m) |
| = | dimensionless coordinates (–) | |
| α | = | inclination angle of the QFN package with respect to the horizontal (°) |
| β | = | air volumetric expansion coefficient (K−1) |
| = | dimensionless nabla operator (–) | |
| = | dimensionless Laplacian operator (–) | |
| ϕ | = | volumetric heat flux (Wm−3) |
| λ | = | air thermal conductivity (Wm−1K−1) |
| µ | = | air dynamic viscosity (Pa s) |
| ρ | = | air density (kg m−3) |
Acknowledgments
The authors are grateful to Clara Ortega, Ania Baïri, David San Martin, and Iken Baïri for their determining help.